No person shall conduct, operate, maintain or allow standing concert attendance at a public assemblage not in a structure except by authority of a Special Permit from the Chief pursuant to Section 57.105.8. Such permit shall be issued only if it is demonstrated to the satisfaction of the Chief that the physical layout of the event and the proposed security measures are adequate to insure that the audience will neither rush the stage, nor gather at the stage in such a manner as to create a dangerous level of crowd density. In evaluating the adequacy of such layout and security, the Chief shall consider the anticipated size, volatility, and behavior of the audience as demonstrated by the past history of like audiences.